1. Field of the Invention
The present invention relates to a work vehicle such as an agricultural tractor having an infinitely variable transmission and an operator actuated selector switch for selecting between manual or automatic engine speed control wherein in the automatic mode, the electronic controller will automatically up shift the transmission and reduce the engine speed to maintain the desired vehicle speed and reduce fuel consumption when the load is reduced and to down shift the transmission and increase the engine speed when the load is reapplied.
2. Description of Related Art
It has been known in work vehicles to provide automatic transmissions with load control to automatically down shift the transmission when the load is increased and to up shift the transmission and reduce the engine speed when the load is reduced to optimize fuel economy.
The present invention improves upon the prior art by providing a means for the operator to select between manual or automatic engine speed control and to select among multiple automatic modes each having a different amount by which the engine speed is reduced when the load is reduced. This enables the operator to match the degree of engine speed reduction to the particular task at hand for improved performance and productivity. In a minimal speed reduction mode, the light load engine speed is only slightly less than the full load speed. However, if the PTO is on, the engine speed will remain at the rated engine speed to provide a constant PTO output speed regardless of the load. This mode is useful when it is necessary to keep the engine speed high regardless of the load, such as when the PTO is operating.
An intermediate speed reduction mode allows for a speed reduction between 62 and 86 percent of the rated engine speed. This mode is useful while doing heavy draft work to enable the engine speed to be reduced at the end of a row but to still maintain sufficient engine speed for other vehicle systems such as the hydraulic system. A maximum speed reduction mode enables the engine speed to be reduced to 57 to 81 percent of the rated engine speed. This mode is useful for light load applications such as transport and hauling operations where the engine speed can be reduced significantly without reducing the vehicle performance. The particular degree to which the engine speed is reduced is set for each mode with the particular speed being set by the vehicle manufacturer. In each mode, the amount of engine speed reduction is proportional to the amount of the load reduction. The speed setting may be changed to customize the speed settings for a given vehicle. Vehicle service facilities can be equipped with the tools to reprogram the electronic controller for the transmission and the engine. In the context of an agricultural tractor, the speeds can be customized to best suit the practices of a given farm.